The present disclosure relates to a phase gating controller and to a control method. In particular, the disclosure relates to a phase gating controller for power control of a load.
A phase gating controller is used to operate a load from an alternating current with variable power. In this case, the load may comprise a predominantly ohmic load, such as a light bulb, or a mixed ohmic and inductive load, such as an electric motor. A thyristor or a triac, which is an interconnection of two thyristors connected back-to-back, is used in order to connect the load to the alternating current. The thyristor has two power terminals, one of which is connected to the load and the other of which is connected to the AC voltage. A control terminal is also provided. The thyristor provides an electrical connection from the first to the second power terminal when a voltage at the control terminal exceeds a predetermined threshold value. This process is known as triggering. The conductivity of the thyristor between the power terminals is then maintained even when the control voltage at the control input is switched off. In order to turn off the thyristor, that is to say to end the conductivity between the power terminals once again, a holding current through the power terminals of the thyristor must decrease below a predetermined threshold value. This is usually the case at every zero crossing of the current.
In order to control the power to the load, the control voltage is not applied to the control input at the beginning of each half-cycle of the AC voltage, but only later. By way of example, it is possible for the instant at which the control voltage is applied to be dependent on a voltage value of the AC voltage at one of the power terminals. The thyristor is then triggered at a predetermined point in the half-cycle and remains switched on until the end of the half-cycle. The later the triggering takes place, the shorter the time in which the load is connected to the alternating-current source and therefore also the lower the power converted in the load.
Owing to vibrations, wear or, if the load is a commutated electric motor, bad commutation, the current flowing through the thyristor/triac can temporarily fall below the holding current, which can lead to the thyristor being turned off if the control voltage at the triggered thyristor is not maintained while the thyristor is conducting. However, maintaining the control voltage causes a certain power loss and may necessitate more expensive wiring of the thyristor. Therefore, the problem addressed by the disclosure is to specify an improved phase gating controller, a method for phase gating control and a corresponding computer program product, by means of which said disadvantages can be avoided. The disclosure solves said problem by means of a phase gating controller, a method for phase gating control and a computer program product having the features disclosed herein.